Hair is viewed to be extremely important in terms of aesthetic appearance. Thus, hair loss caused by congenital or acquired factors is a serious problem for many people. In today's society having a large elderly population and containing numerous sources of stress in particular, there are a growing number of opportunities for being at risk to the loss of scalp hair due to various acquired factors. In order to deal with this situation, various attempts have been made to provide superior hair tonics that more effectively demonstrate hair growth effects including the promotion of hair growth and thicker hair.
Hair follicles are exceptional organs that continue to repeatedly self-regenerate throughout nearly the entire life of a mature living organism. Elucidation of the mechanisms of this self-regeneration are expected to lead to clinical applications for which there are considerable demand, such as hair loss treatment using tissue or cell transplants, and the construction of natural and functionally superior skin sheets containing hair follicles and sebaceous glands. In recent years, research has progressed rapidly on follicular epithelial stem cells (epithelial cells) accompanying the growing interest in stem cell research, and the properties of dermal papilla cells, which are follicle-specific mesenchymal cells, have also been gradually determined. Dermal papilla cells fulfill the role of a so-called control tower that induces activation signals to follicular epithelial stem cells for self-regeneration of hair follicles, and have been determined, along with follicular epithelial stem cells, to be essential cells in follicle reconstruction evaluation systems (Kishimoto, et al., Proc. Natl. Acad. Sci. USA (1999), Vol. 96, pp. 7336-7341: Non-Patent Document 1).
Dermal papilla (DP) and dermal sheath (DS) surrounding the periphery of hair follicles both differ from epithelial cells composing the majority of hair follicles in that they are composed of mesenchymal-derived cell populations. With respect to DS, numerous findings have been reported in recent years suggesting its importance with respect to hair follicle formation. DS has been reported to be regenerated from DP in an experiment involving transplantation of hair bulbs-removed hair follicles of rat whiskers (1), and follicle regeneration has been reported to be induced in mice by transplanting DS of hair follicles from which the lower half has been severed (2). In addition, Jahoda, et al. (Development, 1992, April: 114(4), pp. 887-897: Non-Patent Document 2) reported that follicle regeneration can be induced by transplanting DS to humans (Horne, K. A. and Jahoda, C. A., Development, 1992, November: 116(3), pp. 563-571: Non-Patent Document 3). Moreover, the Tobin, Paus et al. group reported that cells migration occur between DS and DP, and that proliferation of dermal sheath cells (DSc) begins prior to DPc that begin to proliferate during the hair growth phase (Tobin, D. J. et al., J. Invest. Dermatol., 120, pp. 895-904, 2003: Non-Patent Document 4).
In this manner, although DS has a high possibility of fulfilling an important role in the formation of hair follicles, the mechanisms of action have not been well known, and even the properties of DSc are not understood. Therefore, we investigated the gene expression profile that characterizes DSc, and analyzed the properties for the purpose of clarifying the mechanism of action in the follicle formation.